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Endocrine & Cell Communication Part IV: Maintaining Balance () TEACHER NOTES needs coding

1 Endocrine & Cell Communication Part IV: Maintaining Balance (Homeostasis)

AP Biology Curriculum Framework When you ingest your EK 3.D.2 Cells communicate with each other through level rises, which stimulates your direct contact with other cells or from a distance via chemical signaling. to secrete which in turn c. Signals released by one cell type can travel long distances to target cells of another cell type. promotes cellular uptake of glucose into the 2 1. Endocrine signals are produced by endocrine and muscle cells where it is stored as . cells that release signaling molecules, which are specific and can travel long distances through the When your blood level decreases between blood to reach all parts of the body. illustrative example-insulin meals, the pancreas secretes which promotes the hydrolysis of glycogen to release 2 glucose and fatty acids to raise your blood sugar

levels.

Simple Pathways

• are released from an endocrine cell, trave through the bloodstream, and interact with specific receptors within a target cell to cause a physiological response 3

Simple Hormone Pathways

• For example, the release of acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete . The pancreas releases sodium to • This causes target cells in the pancreas, a gland 4 behind the stomach, to raise the pH in the duodenum raise the pH which neutralizes acid chyme from

• The increased pH results in a decrease of secretin the stomach thereby raising the pH (making the secretion. environment more alkaline).

Simple Hormone Pathways In this simple endocrine pathway a low

Pathway Example duodenum pH stimulates endocrine cells in the Low pH in Stimulus duodenum small intestine (S cells) to secrete the hormone

Endocrine S cells of duodenum cell secrete the hormone secretin. Secretin travels through the blood 5 secretin ( ). Hormone stream to its target cells (pancreatic cells) causing them to release bicarbonate solution Negative Blood vessel Target resulting in an increase in the pH. The increase cells Pancreas serves as a negative feedback mechanism Response Bicarbonate release resulting in lower levels of secretin released. Endocrine & Cell Communication: Maintaining Balance (Homeostasis) TEACHER NOTES needs coding

Negative Feedback

• Secretin secretion regulation is an example of negative feedback in action.

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Feedback Regulation

• A negative feedback loop inhibits a response by reducing the initial stimulus, thus preventing excessiv pathway activity. • Positive feedback reinforces a stimulus to produce an even greater response. 7 • For example, in mammals oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin.

An example of positive feedback

Oxytocin stimulates the uterus to contract. This causes the placenta to make more prostaglandins 8 which signal more vigorous uterine contractions which cause more oxytocin to be produced thereby amplifying the contraction process.

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Insulin and Glucagon: Control of Blood Glucose

• Hormones work in pairs to maintain homeostasis. • Insulin (decreases blood glucose) and glucagon (increases blood glucose) are antagonistic hormones that help maintain glucose homeostasis.

9 • The pancreas has clusters of endocrine cells called with alpha cells that produce glucagon and beta cells that produce insulin.

Endocrine & Cell Communication: Maintaining Balance (Homeostasis) TEACHER NOTES needs coding

Figure 45.13 Insulin Body cells take up more Beta cells of glucose. pancreas release insulin into the blood.

Liver takes up glucose and stores it STIMULUS: as glycogen. Blood glucose Blood glucose level rises level declines. (for instance, after eating a -rich meal). Describe the actions that occur when blood

Homeostasis: Blood glucose level glucose levels decline and when they rise. 10 (70–110 mg/100mL) STIMULUS: Blood glucose Blood glucose level Glucagon and insulin are paired hormones that level rises. falls (for instance, after skipping a meal). work together to maintain blood glucose levels

Liver breaks down glycogen Alpha cells of pancrea and releases release glucagon into between 70 and 110 mg/100mL glucose into the blood. the blood. Glucagon

AP Curriculum Framework

• EK 3.D.4 Changes in signal transduction pathways can alter cellular response. – A. Conditions where signal transduction is blocked or defective can be deleterious, preventative or 11 prophylactic. • Illustrative example -

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Out of Balance: Diabetes Mellitus

• Diabetes mellitus is perhaps the best-known endocrine disorder. Ask students to explain how a lack of insulin • It is caused by a deficiency of insulin or a decreased response to insulin in target tissues. leads to elevated levels of glucose in the blood. 12 • It is marked by elevated blood glucose levels. Then ask them to suggest reasons this increased level of glucose is harmful to the person with diabetes.

Out of Balance: Diabetes Mellitus

• mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells. Type 1 has in the past been referred to as Juvenile Diabetes. Just as a point of interest, the • mellitus (non-insulin-dependent) 13 involves insulin deficiency or reduced response of incidence varies from 8 to 17 per 100,000 in target cells due to change in insulin receptors. Northern Europe and the U.S. with a high of about 35 per 100,000 in Scandinavia to a low of 1 per 100,000 in Japan and China.

Action of Insulin When insulin receptors respond properly to the presence of insulin, the result is the transport of glucose from outside the cell to inside the cell 14 via transport protein. People with Type I diabetes do not produce sufficient insulin to maintain a proper level of glucose transport. The disorder is typically treated by providing the patient with insulin. 14 Endocrine & Cell Communication: Maintaining Balance (Homeostasis) TEACHER NOTES needs coding

Insulin & Glucose Regulation

15 Scroll across the bottom of the to activate the animation controls and press PLAY

Increases Ca2+ Active 2+ uptake in vitamin D Stimulates Ca intestines uptake in kidneys

PTH Blood calcium levels need to be approximately Parathyroid Stimulates gland (behind 2+ 16 Ca release thyroid) 10 mg/100 mL. Two hormones, PTH and from

2+ STIMULUS Blood Ca Falling blo calcitonin work in tandem to regulate the blood level rises. + Ca2 leve glucose in mammals. Homeostasis: Blood Ca2+ level (about 10 mg/100 mL)

Homeostasis in blood calcium levels

• PTH increases the level of blood Ca2+ – It releases Ca2+ from and stimulates reabsorption of Ca2+ in the kidneys. Describe how calcitonin and PTH work together to maintain blood calcium levels. High calcium – It also has an indirect effect, stimulating the kidne 17 to activate vitamin D, which promotes intestinal levels can cause mental confusion, nausea, uptake of Ca2+ from food. fatigue. Low blood calcium causes muscle • Calcitonin decreases the level of blood Ca2+ – It stimulates Ca2+ deposition in bones and secretio cramps, spasms, twitching and tingling in the by kidneys. fingers and around the mouth.

Homeostasis In Blood Calcium Levels This animation has more detail than we actually need. The next is illustrative of the amount of detail students need to know. Emphasize it is the 18 “homeostasis” aspect of this process established by cell to cell communication that is important.

Scroll across the bottom of the to activate the animation controls and press PLAY

Endocrine & Cell Communication: Maintaining Balance (Homeostasis) TEACHER NOTES needs coding

Practice

• Blood calcium levels

• Blood calcium level

• Parathyroid release

• Thyroid releases calcitonin Ask students to match the events on the right 19 • If calcium rises abov point with the numbers in the picture. The next shows • If calcium falls below point the answers.

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Solution

1. Blood calcium levels r

3. Blood calcium level fa

5. Parathyroid releases P 2. Thyroid releases calci The two hormones, calcitonin and parathyroid 6. If calcium rises above 20 point hormone work together to keep blood calcium 4. If calcium falls below point levels within a homeostatic range.(10 mg/100 mL)

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Created by:

Debra Richards 21 Coordinator of Secondary Science Programs Bryan ISD Bryan, TX